Prognostic value of perfusion- and diffusion-weighted MR imaging in first 3 days of stroke

The aim of this study was to evaluate the differences in cerebral perfusion seen on mean transit time (MTT) and cerebral blood volume (CBV) maps and to assess the subsequent prognostic value of the MTT–DWI (diffusion-weighted MRI) and CBV–DWI mismatch in the first three days of stroke on lesion enlargement and clinical outcome. In 38 patients, imaged 1–46 h after onset of symptoms, lesion volumes on proton-density (PD)-weighted MRI, DWI and PWI (both MTT and CBV maps) were compared with lesion volumes on follow-up PD-weighted scans, and to clinical outcome (National Institutes of Health Stroke Scale, Barthel index, and Rankin scale). The MTT-CBV, MTT–DWI and CBV–DWI mismatches were compared with change in lesion volume between initial and follow-up PD-weighted scans. Lesion volume on both DWI and PWI correlated significantly with clinical outcome parameters (p < 0.001) with strongest correlation for lesion volume on CBV. Perfusion–diffusion mismatches were found for both CBV and MTT and correlated significantly with lesion enlargement on PD-weighted imaging with strongest correlation for the CBV–DWI mismatch. The CBV–DWI mismatch has the highest accuracy in predicting lesion size on follow-up imaging and in predicting clinical outcome. Lesion volume measurements on CBV maps have a higher specificity than on PD-weighted, MTT or DWI images in predicting clinical follow-up imaging and in predicting clinical outcome. Received: 21 January 2000; Revised: 18 April 2000; Accepted: 20 April 2000     

MRI in acute subarachnoid haemorrhage; findings with a standardised stroke protocol

There is doubt as to whether acute haemorrhage is visible on MRI. We carried out MRI within 6 h of symptom onset on five patients with minor (low Hunt and Hess grades 1 or 2) subarachnoid haemorrhage (SAH) diagnosed by CT to search for any specific pattern. We used our standard stroke MRI protocol, including multiecho proton density (PD)- and T2-weighted images, echoplanar (EPI) diffusion- (DWI) and perfusion- (PWI) weighted imaging, and MRA. In all cases SAH was clearly visible on PD-weighted images with a short TE. In four patients it caused a low-signal rim on the T2*-weighted source images of PWI, and DWI revealed high signal in SAH. In the fifth patient SAH was perimesencephalic; susceptibility effects from the skull base made it impossible to detect SAH on EPI DWI and T2*-weighted images. Perfusion maps were normal in all cases. MRA and conventional angiography revealed an aneurysm in only one patient. Stroke MRI within 6 h of SAH thus shows a characteristic pattern.     

Diffusion- and perfusion-weighted MRI in a patient with a prolonged reversible ischaemic neurological deficit

We report acute and follow-up diffusion- and perfusion-weighted MRI (DWI, PWI) findings in a patient with a prolonged reversible ischaemic neurological deficit. PWI 12 h after the patient was last seen to be without symptoms revealed a large perfusion deficit in the left posterior MCA territory with a relatively inconspicuous and much smaller abnormality on DWI. Follow-up showed resolution of abnormalities on both DWI and PWI, and conventional MRI was normal, apart from a very slight abnormality, visible only on FLAIR images, at the centre of the initially DWI-positive region. These findings demonstrate the utility of PWI when be used in combination with DWI to investigate the pathophysiology of transient ischemic syndromes. Received: 26 July 1999/Accepted: 20 September 1999     

脑梗死前期MR脑灌注成像和弥散成像诊断的研究

目的:研究提高对脑梗死前期的诊断水平,减少脑梗死的发生。材料和方法:由于对比增强磁共振脑灌注成像在脑缺血诊断中具有较为敏感的特点,用此技术及弥散加权和常规MRI技术对18例脑缺血患者和20例非脑血管病患者进行脑梗死前期诊断的对比分析研究。结果:在T1WI、T2WI、FLAIR、MRA、DWI和PWI六种MR成像技术中,仅有脑灌注成像可以检出脑梗死前期病例,余均不能检出。结论:脑梗死前期的MR灌注成像可有效地检出脑梗死前期病例,是目前比较理想的功能性磁共振检查方法。     

Symptomatic vasospasm after subarachnoid haemorrhage: assessment of brain damage by diffusion and perfusion-weighted MRI and single-photon emission computed tomography

Our purpose was to assess the usefulness of diffusion- and perfusion-weighted MRI for the detection of ischaemic brain damage in patients with suspected vasospasm after subarachnoid haemorrhage (SAH). We studied 11 patients admitted with a ruptured aneurysm of the anterior circulation and suspected of intracranial vasospasm on clinical examination and transcranial Doppler sonography (TCD). All were investigated by technetium-hexamethyl-propylene amine oxime (Tc-HMPAO) single photon emission computed tomography (SPECT) and diffusion and perfusion-weighted MRI (DWI, PWI) within 2 weeks of their SAH. Trace images and TTP maps were interpreted by two examiners and compared with clinical and imaging follow-up. PWI revealed an area of slowed flow in seven patients, including four with major and three with minor hypoperfusion on SPECT. In two patients, PWI did not demonstrate any abnormality, while SPECT revealed major hypoperfusion in one and a minor deficit hypoperfusion in the other. Two patients with high signal on DWI had a permanent neurological deficit.     

Serial diffusion-weighted imaging in MELAS

Clinical features of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) resemble those of cerebral infarcts, but the pathogenesis of infarct-like lesions is not fully understood. To characterise these infarct-like lesions, we studied two patients with MELAS using diffusion-weighted (DWI) MRI before and after stroke-like episodes and measured the apparent diffusion coefficient (ADC) in the new infarct-like lesions. These gave high signal on DWI and had much higher ADC than normal-appearing regions. The ADC remained high even 30 days after a stroke-like episode then decreased in lesions, with or without abnormality as shown by conventional MRI. We speculate that early elevation of ADC in the acute or subacute phase reflects vasogenic rather than cytotoxic edema. The ADC of the lesions, which disappeared almost completely with clinical improvement, returned to normal levels, which may reflect tissue recovery without severe damage. To our knowledge, this is the first study of DWI in MELAS. Received: 13 September 1999/Accepted: 7 January 2000     

Perfusion-weighted MRI as a marker of response to treatment in acute and subacute stroke

We carried out baseline and short-term follow-up MRI, including perfusion-weighted imaging (PWI) and tests of neurologic and cognitive function on 15 consecutive patients with large-vessel ischemic stroke who showed a persistent large perfusion-diffusion mismatch at enrollment up to seven days after the onset of symptoms. Of these, ten underwent induced blood pressure elevation with phenylephrine and oral medications (in eight) or intravenous fluids (in two) with the goal of improving perfusion; five had no such treatment. Significant functional improvement was defined by a reduction of 3 or more points on the NIH stroke scale (NIHSS). Significant improvement in perfusion was defined by a reduction in the volume of hypoperfused brain by 30 cc on PWI using time-to-peak (TTP) maps, without enlargement of the infarct. There was a strong, statistically significant association between improved function and improved perfusion: six (75%) of eight patients who improved in function, but none of the seven who did not, showed a reduction in volume of hypoperfused brain. All six patients who met the perfusion goal, and only two (22%) of nine who did not showed significant functional improvement (Fishers exact: P <0.01). There were no differences between patients who improved functionally and those who did not with respect to age, initial volume of abnormality on DWI or PWI, initial NIHSS, or changes on DWI. These findings indicate that reduction in volume of hypoperfused brain on PWI is a marker of response to treatment to improve perfusion even in subacute stroke and that partial reperfusion of regions of salvageable but dysfunctional tissue is a mechanism of improved function associated with induced blood pressure elevation.     

磁共振DWI和PWI在超急性脑梗死诊治中的应用

目的评价磁共振弥散加权成像（DWI）和灌注加权成像（PWI）在超急性脑梗死诊断及指导临床早期溶栓治疗中的应用价值。方法 56例发病在6 h以内且临床提示处于超急性期脑梗死患者均行急诊MRI检查,扫描序列包括T1WI、T2WI、FLAIR、DWI及PWI,部分病例行MRA检查。结果 56例患者T1WI均未见异常信号,35例患者T2WI、FLAIR发现有轻微异常信号影。56例DWI和PWI均发现异常,但在DWI上显示的高信号急性脑梗死区域与在PWI上显示的脑灌注延长区域不匹配,PWI显示的病灶范围更大。图像后处理显示平均通过时间（MTT）、达峰时间（TTP）均有不同程度的延长,脑血流量（CBF）出现不同程度的减少。结论急诊MRI,特别是DWI和PWI序列对超急性脑梗死患者可以作出准确的诊断,可以安全、迅速、有效地指导临床进行早期溶栓治疗。     

急性脑缺血再灌注DWI及PWI的实验研究

目的:评价DWI及PWI判定急性脑梗死诊断及缺血半暗带的作用。材料和方法:40只SD大鼠随机均分4组,A组作假手术对照;B、D组分别栓塞2h、6h,均再灌注2h、24h;C组栓塞2h再灌注24h、7d。B、C、D组于各自栓塞及再灌注时间点行DWI、PWI及常规序列扫描;后处理获得表观扩散系数(ADC)、脑血容量(CBV)、脑血流量(CBF)、平均通过时间(MTT)形态图。并将结果与四氮唑红(TTC)染色和病理作比较。结果:A组DWI、PWI、TTC染色及病理观察均无异常;B、C、D组栓塞时均可见右大脑中动脉供血区DWI呈高信号,D组异常信号区面积明显大于B组,病理电镜表现为细胞内水肿。B、D组再灌注24hDWI异常信号区面积与灌注前相比,B组无明显变化,D组较前增大;C组再灌注7d6只大鼠DWI见高信号,但ADC图均正常。B、D组栓塞时右大脑中动脉供血区PWI灌注缺损区面积相似。B组PWI异常信号面积大于DWI异常信号区;D组PWI与DWI异常信号面积无明显差别。结论:DWI能灵敏反映急性期缺血脑组织损伤情况,PWI能灵敏反映组织血流灌注情况。DWI、PWI联合应用有可能判定缺血半暗带。     

Usefulness of diffusion/perfusion-weighted MRI in rat gliomas: correlation with histopathology

RATIONALE AND OBJECTIVES: Diffusion/perfusion-weighted MRI (DWI/PWI) can provide additional useful information in the diagnosis of patients with brain gliomas in a noninvasive fashion. However, the exact role of these new techniques is still undergoing evaluation. Our hypothesis was that DWI and PWI could be useful for assessment of growth and vascularity of implanted C6 rat gliomas. MATERIALS AND METHODS: Thirty-six rats were implanted with C6 glioma cells intracerebrally. Between 1 and 4 weeks after implantation, 8-10 rats were imaged on a clinical, 1.5-T whole-body magnetic resonance system with T(1)-weighted imaging (T(1)WI), T(2)-weighted imaging, DWI, PWI, and postcontrast T(1)WI at each weekly time point. All tumors were examined histologically; tumor cellularity and microvascular density were counted. RESULTS: On DWIs, statistical differences of apparent diffusion coefficient values for both the tumoral core and peritumoral region were present comparing tumors of 3-4 weeks' growth with tumors of 1-2 weeks' growth. Apparent diffusion coefficient value of tumoral core was negatively correlated with tumor cellularity (r = -0.682, P < .01). Statistical difference of maximal regional cerebral blood volume of tumoral core was present comparing 2-4 weeks with both 1 week after implantation and contralateral white matter (P < .01). Native vessel dilation in regions of normal brain at the periphery of the tumors at 1 week after implantation was observed. Correlation between maximal regional cerebral blood volume of tumor core and microvascular density was present (r = 0.716, P < .01). CONCLUSION: DWI and PWI has potential to characterize C6 gliomas in rats, which is a promising model similar to human gliomas.     

Diffusion- and perfusion-weighted MR imaging in a patient with acute demyelinating encephalomyelitis (ADEM).

To monitor changes of brain tissue metabolism in acute demyelinating encephalitis (ADEM), we examined a patient with suspected ADEM by serial MRI including diffusion- and perfusion-weighted imaging (DWI, PWI). Within the inflammatory tissue, the apparent diffusion coefficients were reduced, normal, and increased. Perfusion varied between reduced and normal values, except for small hyperperfused regions. Combining standard MRI with DWI and PWI may elucidate different overlapping phases in cerebral inflammation.     

Cerebral abscesses: investigation using apparent diffusion coefficient maps

The combination of high signal and reduced apparent diffusion coefficients (ADC) within abscesses on diffusion-weighted MRI (DWI) has been reported as characteristic of abscesses, and useful for distinguishing them from cystic or necrotic neoplasms. To assess whether these are consistent findings in abscesses, we used DWI-derived ADC to investigate changes in water diffusibility in cerebral abscesses. We reviewed the MRI studies and clinical records of five patients with brain abscesses, who underwent DWI. Regions of interest were drawn within the abscesses on ADC maps, to obtain the ADC. The center of all five abscesses gave signal higher than that of white matter on DWI. The three largest also appeared bright on ADC maps, i. e., showed ADC substantially lower than those of normal white matter, consistent with restricted diffusion. However, the two smaller abscesses were not visible on ADC maps because their ADC were essentially the same as that of white matter; they did not show restricted diffusion. The absence of restricted diffusion within small abscesses may be related to intrinsic differences in molecular microenvironment between small and large abscesses, or to greater influence of volume averaging with surrounding edema on the ADC in smaller abscesses. Received: 22 May 2000 Accepted: 9 July 2000     

大鼠右肝血供不同程度阻断后的病理变化及磁共振表现

目的:探讨用磁共振新技术活体检测肝细胞凋亡和坏死的可能性。方法:①体重为0.25～0.3kg的SD大鼠90只随机分成A、B、C三组,每组30只,分别行右肝门静脉结扎(A组)、右肝门静脉及肝动脉双结扎(B组)及假手术(C组),术后3h、1天、3天、7天、14天作为5个时间点,各观察6只。②每组大鼠进行磁共振成像(MRI)、磁共振扩散加权成像(DWI)、1H磁共振波谱(1H-MRS)及磁共振灌注成像(PWI)检查。③取肝脏标本行病理学及电镜检查。④将磁共振检查结果同病理学及电镜对照分析。结果:①A组病理学及电镜检查证实肝细胞发生凋亡;B组肝组织发生凝固性坏死。②A组T1WI信号增高,T2WI信号刚开始略减低,后呈小片状增高;DWI呈小片状高信号,表观扩散系数(ADC)图则相反;MRS表现为胆碱(Choline,Cho)、肌酸(Creatine,Cr)、谷氨酸(Glutamate,Glx)峰稍下降,乳酸(Lactate,Lac)峰、脂质(Lipid,Lip)峰增加;PWI灌注曲线下降;③B组T1WI信号减低,T2WI信号增高;DWI呈高信号;Cho峰下降明显,Cr、Glx峰下降,Lac峰明显升高,Lip峰略增高;PWI曲线低平。结论:右肝血供不同程度阻断后肝细胞分别发生凋亡和坏死;磁共振检查(DWI、MRS、PWI)具有特征性表现,可活体检测细胞凋亡和坏死的存在。     

The value of diffusion-weighted imaging for prediction of lasting deficit in acute stroke: an analysis of 134 patients with acute neurologic deficits

Acute stroke is one of the three major causes of death and disability in the United States. Now that new, and possibly effective therapy is becoming available, accurate, rapid diagnosis is important to provide timely treatment, while avoiding the risk of complications from unnecessary intervention. Our objective was to test the hypothesis that use of echo-planar (EPI) diffusion-weighted imaging (DWI) is more accurate than conventional T₂ weighted MRI in predicting progression to stroke in patients with acute ischemic neurologic deficits. We studied 134 patients presenting with acute neurologic deficits to a community hospital emergency room with both conventional MRI and DWI within 72 h of the onset of the acute deficit. We found DWI significantly more sensitive to permanent neurologic deficit at discharge (sensitivity 0.81) than conventional MRI (sensitivity 0.41). When available, DWI should be considered for routine use in patients being imaged for acute stroke. Received: 21 January 2000 Accepted: 7 October 2000     

MRI弥散和灌注成像诊断超早期脑梗死的实验研究

目的评价磁共振弥散成像(DWI)和灌注成像(PWI)技术在超早期脑梗死中的诊断价值。方法新西兰白兔42只,随机分为7组,其中6组为实验组,1组为假手术组。采用改良O’Brein法闭塞兔一侧大脑中动脉制作局灶性脑缺血模型,对照组仅暴露同侧大脑中动脉,不予电凝。术后0.5、1、2、3、4、6 h不同时间段进行MRI扫描。结果常规MR序列显示缺血病灶明显晚于DWI和PWI。随着时间延长病灶各参数有特征性变化规律。在DWI和PWI中缺血区体积均随时间的延长不断扩大,两者不匹配区随时间延长逐渐缩小。结论DWI和PWI在诊断超早期脑梗死上优于常规MR序列。     

低场MR扩散加权成像在超急性期脑梗死诊断中的应用

目的 :评价低场MR扩散加权成像 (DWI)在超急性期脑梗死 (HCI)诊断中的应用价值。方法 :对起病时间 6h内临床拟诊脑梗死的 12例患者使用 0 .2T磁共振仪行DWI和常规MRI扫描。结果 :DWI诊断HCI 8例 ,DWI阴性 4例 ;常规MRI扫描 2例符合脑梗死诊断 ,10例不符合 ,最终临床诊断为HCI 8例。DWI所见异常高信号区在以后的CT或MR随访中均见明显梗死病灶。结论 :低场DWI在HCI诊断中能得到成功运用 ,且诊断高度准确。     

脑缺血再灌注大鼠模型FAIR-PWI研究

目的:探讨流动敏感交替反转恢复序列灌注成像(FAIR- PWI)对大鼠脑缺血后再灌注的评价.方法:使用GE 3.0T MRI成像仪,在完成T1WI、T2WI、弥散加权成像(DWI)和FAIR - PWI序列后,对SD大鼠行暂时性右侧大脑中动脉闭塞(TMCAO)手术,分别在脑缺血3h和再灌注3h及21h行重复上述MRI检查;最后进行病理学TTC染色观察梗死区域及范围.结果:TMCAO后3h时,患侧大脑半球DWI信号升高、FAIR - PWI灌注增加、且皮质相对脑血流量(rCBF)大于基底节区;再灌注3h及21h后,患侧大脑半球DWI信号面积(0.63±0.1.2cm2、0.48±0.23cm2)仍高于FAIR - PWI高灌注面积(0.51±0.26cm2、0.34±0.44cm2,P=0.01),皮质及基底节区rCBF较缺血时增加.TTC染色示梗死面积(0.42±0.78cm2)小于DWI异常信号面积,而大于FAIR - PWI高灌注面积,且梗死区以基底节为主.结论: FAIR- PWI结合DWI能对早期缺血再灌注进行动态观察及半定量测量,可能为临床溶栓治疗方案的预后判断和随访提供重要参考.     

Comparison of CT with diffusion-weighted MRI in patients with hyperacute stroke

Tissue changes in ischaemic stroke are detectable by diffusion-weighted MRI (DWI) within minutes of the onset of symptoms. However, in daily routine CT is still the preferred imaging modality for patients with acute stroke. Our purpose of this study was to determine how early and reliably ischaemic brain infarcts can be identified by CT and DWI. Three neuroradiologists, blinded to clinical signs but aware that they were dealing with stroke, analysed the CT and DWI of 31 patients with an acute ischaemic stroke. We calculated k-values to analyse inter-rater variability. The ratings were compared with follow-up studies showing the extent of the infarct. The combined assessment of all observers gave positive findings in 77.4 % of all CT examinations, with k = 0.58. Areas of high signal were seen on all DWI studies by all observers (k = 1). Estimation of the extent of the infarct based on DWI yielded k = 0.70 and that based on CT k = 0.39. DWI was much more reliable than CT in the detection of early ischaemic lesions and we believe that it should be used in acute ischaemic stroke before aggressive therapeutic intervention. Received: 11 August 2000 Accepted: 29 November 2000     

Relationship between sodium intensity and perfusion deficits in acute ischemic stroke

Purpose

To assess the relationship between sodium signal intensity changes and oligemia, measured with perfusion‐weighted imaging (PWI), in ischemic stroke patients.

Materials and Methods

Nine ischemic stroke patients (55 ± 13 years), four with follow‐up scans, underwent sodium and proton imaging 4–32 hours after symptom onset. Relative sodium intensity was calculated as the ratio of signal intensities in core (identified as hypertintense lesions on diffusion‐weighted imaging [DWI]) or putative penumbra (PWI‐DWI mismatch) to contralateral homologous regions.

Results

Sodium intensity increases in the core were not correlated with the severity of hypoperfusion, measured with either cerebral blood flow (rho = 0.157; P = 0.61) or cerebral blood volume (rho = ?0.234; P = 0.44). In contrast, relative sodium intensity was not elevated (4–7 hours 0.96 ± 0.07; 17–32 hours 1.00 ± 0.07) in PWI‐DWI mismatch regions.

Conclusion

Sodium signal intensity cannot be predicted by the degree of hypoperfusion acutely. Sodium intensity also remains unchanged in PWI‐DWI mismatch tissue, indicating preservation of ionic homeostasis. Sodium magnetic resonance imaging (MRI), in conjunction with PWI and DWI, may permit identification of patients with viable tissue, despite an unknown symptom onset time. J. Magn. Reson. Imaging 2011;33:41–47. © 2010 Wiley‐Liss, Inc.

     

磁共振扩散加权成像对结肠癌术后肝转移灶检出的临床研究

目的:探讨磁共振扩散加权成像对结直肠癌肝转移的诊断价值。方法:27例结直肠癌患者行肝脏磁共振扩散加权成像、非增强磁共振和多层CT检查。阅片前告知阅片者患者为结直肠癌术后,但不提供临床病史和既往影像学资料。结果:多层CT、非增强磁共振和扩散加权成像对肝转移灶的敏感度分别为72%(45/63)、76%(48/63)和93%(58/63),扩散加权成像对肝转移灶具有更高的敏感度且与多层CT和非增强MRI相比,差异有显著性意义。扩散加权成像对肝转移患者敏感度最高(82%),而多层CT和非增强MRI分别为77%和66%。结论:磁共振扩散加权成像对结直肠癌肝转移灶的检出率高于多层CT和非增强MRI。